1) Field of the Invention
The present Invention relates to an optical system supporting device for use in an optical information recording apparatus in which the optical information is recorded on an information recording medium such as an optical disc and an optical card by illuminating a light beam thereon.
2) Prior Art Statement
When illuminating the light beam on the information recording medium in order to record the optical information thereon, a focusing control and a tracking control of the light beam are necessary with respect to tracks formed on the recording medium. For the purpose of the focusing and tracking control of the light beam, an objective lens, which is arranged at an opposite side of the recording medium, should be smoothly moved in a focusing direction and a tracking direction.
The objective lens is supported by a lens holder, i.e. an optical system supporting device; and the movement thereof is conducted by moving the lens holder in the focusing and tracking directions. Such optical system supporting device is, for instance, disclosed in Japanese Patent Preliminary Publication No. 59-221839. FIG. 1 is a schematic perspective view showing the optical system supporting device disclosed in this publication. An objective lens 21 is held in an objective lens holder 22; and the lens holder 22 is arranged on a base plate 23. At both sides of the base plate 23 in a tangential direction, are arranged fixing members 24, 24. It should be noted that in this specification a tracking direction is represented by X direction, a tangential direction by Y direction and a focusing direction by Z direction, hereinafter. On inner walls of these fixing members 24, 24, magnets are provided, respectively. Between one of the fixing members 24 and the lens holder 22, four metal wires 25 are extended in parallel with Y direction. The wires 25 are arranged parallel to each other; and each end of these wires is secured to the fixing member 24 and the lens holder 22. Therefore, the lens holder 22 is supported by the wires 25 so as to be movable in the focusing and tracking directions.
In Japanese Patent Preliminary Publication No. 60-197942, there is disclosed another optical system supporting device. FIG. 2 is a perspective view depicting a structure of this device. In this device, the lens holder 27 holding an objective lens 28 therein is supported by four metal wires 29, 30, 31 and 32. As shown in FIG. 2, the wires 29 and 30 are extended in the Y direction, and the wires 31 and 32 are extended in the X direction; and one end of each wire is fixed to fixing members 33 and 34 arranged on a base plate 35. In this device, the lens holder 27 is also arranged to be movable in the focusing and tracking directions.
A critical commercial demand of an optical information recording apparatus having such optical system supporting device is that it be made small in size. Therefore, the optical system supporting device is also required to be made small in size. Further, in the optical information recording apparatus, it is required to expand a range over which the information can be recorded on the recording medium and the information recorded thereon can be read out therefrom. In order to expand the recording/reproducing range, the size of the supporting device in the tracking direction particularly should be made small.
However, in the conventional device shown in FIG. 1, there are provided tracking coils 26 at both sides in the Y direction of the lens holder 22; and the wires 25 are arranged outside one of the tracking coils 26 straightly. Therefore, the width of the lens holder 22 in the Y direction is determined according to the width of the tracking coil 26 and thus the width of the lens holder can not be made small. It may be suggested to bend the tracking coil 26 into an L shape in order to make the width of the lens holder 22 small, but a number of assembling processes of the pick up device would be increased.
On the other hand, the conventional device denoted in FIG. 2, succeeds in making the width (in the X direction) of the lens holder 27 per se small, so that the lens holder 27 can be arranged in the vicinity of a spindle motor (not shown), which is provided for driving the pick up device as a whole. However, between the lens holder 27 and the fixing member 34, there are extended the metal wires 31 and 32 in the X direction, and thus the size in the X direction of the device as a whole becomes large. The information recording medium is generally stored in a cartridge, and in the cartridge, there is provided an opening for passing a light beam therethrough. Therefore, when the lens holder 27 is moved in the X direction, the fixing member 34 makes contact with the opening of the cartridge, so that recording and read out of information at an outer portion of the recording medium could not be conducted.